Cylindrical robots are used for picking and placing objects in a variety of applications including in wafer transfer systems in semiconductor processing. Their axes form a cylindrical coordinate system with the robot arms having radial, rotational and vertical motion. Robots that have greater than 360° rotation improve throughput by allowing objects to be picked and placed using a minimum or reduced number of moves than required with robots that have a range of motion of 360° or less.
Continuous rotation functions well for optimized robot motion and throughput but requires an electrical and pneumatic slip ring assembly. Standard cables through the shoulder also cannot be used, as rotating over 360° will lead to breakage and or entanglement of the cables. Hardstop assemblies are used to prevent over-rotation of the arm, so that cables and tubings through the shoulder are not over-rotated past their functional limit. To prevent rotation over 360°, a structural feature is provided to engage with another structural feature that rotates along with the arm. By engaging, the arm is prevented from over-rotating in either direction. As a result, it may be necessary to reverse course and travel longer paths (e.g., to get from 260° to 10°, it is necessary to travel 250°, rather than 110°). This also limits a robot's accessible range within an environment. Moving hardstops may be used to provide non-continuous rotation over 360°.